1. Field of the Invention
This invention relates to a magnetic recording medium and a data reproducing apparatus. More particularly, it relates to a magnetic disk etc. in which the patterns of magnetization specifying the address information for specifying data-recording tracks represent the Grey code between neighboring tracks, and a data reproducing apparatus for reproducing data from the magnetic recording medium.
2. Description of the Related Art
In magnetic disk or floppy disk devices, a magnetic disk is employed as a magnetic recording medium. On the magnetic disk, there are formed a large number of concentrically or spirally extending data-recording tracks. Each track is divided into plural sectors in the circumferential direction. Consequently, in the magnetic disk, it is possible to specify the area for data recording or reproduction by specifying the track number, referred to herein as a track address, and a sector number, referred to herein as a sector address.
As a control system in which the recording head or the playback head is positioned in the radial direction R of the magnetic disk and holding the head at the center of a track having the targeted track address (on-track condition), there has been known a sector servo system in which the positioning servo pattern is time-divisional recorded, along with usual data, on the recording surface of the magnetic disk.
Specifically, a servo region (servo zone) is provided between neighboring sectors on the same track. In the servo zone, a track address used for rough positioning during the seek operation and a fine pattern for maintaining the on-track condition are recorded as servo patterns. The track addresses are formed in alignment with one another in a direction perpendicular to the track direction.
In general, data are recorded as inversion of magnetization, and Grey code is frequently employed as the track addresses. Specifically, the track addresses of the Grey code are extensively used in a magnetic disk. That is, the track addresses are recorded in each track by inverting the direction of magnetization in association with each bit of the Grey code. The Grey code is used for the track addresses since a code recorded in a given track differs from a code recorded on the track neighboring thereto by only one bit, so that, when the playback head traverses two tracks, the value reproduced by the playback head indicates one of the addresses of the two tracks, which is convenient for the seeking operation.
When a code such as the Grey code is employed as the track address for the magnetic disk, it is required for the code to satisfy the following requirements.
If the inversion of magnetization occurs at the same circumferential positions of the neighboring tracks, the direction of inversion of magnetization must be the same in order to prevent interference of the magnetic flux and to enable the change in the magnetic flux correctly when the playback head traverses the tracks.
With the use of a Grey code not satisfying this requirement, if, when the playback head during seeking traverses a track and has passed through a mid portion of the neighboring track, the playback signal for the track address is converted by threshold or peak detection into binary data, there is produced a value totally irrelevant to either track addresses due to the slightest noise. In addition, such value does not have the characteristics of the Grey code.
As the code satisfying the above requirement has been proposed by the present Assignee in the U.S. Pat. No. 5,274,510 which describes a Grey-like code converted from the Grey code or a code comprising the Grey-like code with a dummy bit appended thereto.
The use of the above-mentioned Grey code or the code comprised of the Grey-like code and the dummy bit leads to increased redundancy and hence to increased area required for recording the track address.
That is, if the Grey-like code etc is used, a recording area which is 1.5 to 2 times the area for recording the number of bits required for a track address is required, thus decreasing the data recording capacity of the magnetic disk.
In view of the above-described status of the art, it is an object of the present invention to provide a magnetic recording medium and a data reproducing apparatus whereby the address information may be reliably reproduced with the use of a required number of bits without the necessity of adding redundancy to the address information for specifying the track even during the seek operation when the playback head traverses the track.
In one aspect, the present invention provides a magnetic recording medium in which the address information for specifying a track for data recording is recorded as the direction of magnetization, wherein the direction of magnetization corresponding to the address information represents the Grey code between neighboring tracks.
In another aspect, the present invention provides a magnetic recording medium in which the address information for specifying a track for data recording is recorded as magnetization or non-magnetization, wherein magnetization or non-magnetization corresponding to the address information represents the Grey code between neighboring tracks.
In a terminal region of the address information, terminal information formed by a predetermined direction of magnetization or magnetization or non-magnetization is recorded.
In still another aspect, the present invention provides a data reproducing apparatus comprising: a magnetic head for detecting reproduced signals from a magnetic recording medium in which the address information for specifying a track for data recording and the terminal information of the address information are recorded as the direction of magnetization, wherein the direction of magnetization corresponding to the address information represents the Grey code between neighboring tracks; and maximum likelihood decoding means for maximum likelihood decoding reproduced signals from said magnetic head for reproducing the address information.
In yet another aspect, the present invention provides a da reproducing apparatus comprising: a magnetic head for detecting reproduced signals from a magnetic recording medium in which the address information for specifying a track for data recording and the terminal information of-the address information are recorded as magnetization or non-magnetization, wherein magnetization or non-magnetization corresponding to the address information represents the Grey code between neighboring tracks, and maximum likelihood decoding means for maximum likelihood decoding reproduced signals from said magnetic head for reproducing the address information.
According to the present invention, the address information for specifying data-recording tracks is recorded on the magnetic recording medium so that the direction of magnetization or the condition of magnetization or non-magnetization corresponding to the address information and the terminal information represents the Grey code between neighboring tracks. The reproduced signals of the address information and the terminal information are maximum likelihood decoded for reproducing the address information and the terminal information corresponding to the direction of magnetization or magnetization/non-magnetization. This enables the address information to be decoded more reliably without increasing redundancy to the number of bits required as the address information whole the properties as the Grey code are maintained.